SARS pandemic a worry, but now it's wait and see

Virus unpredictable, may grow stronger or weaker as it spreads, scientists say

With victims in 26 countries, including four regions of China, the mysterious flu-like illness known as SARS has scientists increasingly worried about the spectre of a worldwide pandemic.

There is always a chance that severe acute respiratory syndrome, which has killed at least 170, will fizzle out on its own. Or it could become a disease we learn to live with, like the flu.

But medical professionals, particularly those on the front lines, worry that the new coronavirus that causes SARS is proving too wily a foe.

Initially they thought it spread only through tiny droplets coughed into the air by the infected. But Hong Kong health authorities, who have one of the worst epidemics on their hands, now believe that in at least one case, it spread through a leaky sewage system, infecting hundreds in a single apartment building.

Once thought to be defeated in Canada by quarantine, SARS popped up this week in a Scarborough, Ontario, condominium complex and spread through a Catholic prayer meeting, infecting at least 30.

"We're not out of the woods yet," said Dr. Donald Low, microbiologist in chief at Toronto's Mount Sinai Hospital, "This is a different animal than I've ever seen before."

The vastness of China, where the disease first surfaced, presents one major test of whether SARS or public health authorities will win.

"We can't make any predictions until we understand what is going on in China," said Dr. David L. Heymann, the World Health Organization's communicable diseases director.

But many believe Toronto is a barometer of whether aggressive public health efforts can halt the spread of the disease. More than 7,000 people there have been quarantined at home for 10 days at some point over the past month .

"If they can't take it out with the measures they're taking, then I don't think they can contain it in Third World countries," said Dr. Arnold Monto, a University of Michigan epidemiology professor.

Tricky to define

Defining when an epidemic becomes a pandemic is tricky business - even among scientists. In general, a disease crosses that line when it causes severe illness and has spread pervasively through multiple countries or jumped continents.

As of yesterday, SARS had struck at least 3,461 worldwide. That includes 208 suspected cases in the United States, although authorities here say 35 cases fit the WHO's strict definition of SARS.

Twenty countries have reported fewer than 10 cases. Still, the first reported case in India, initial cases in South America, a growing number in Hong Kong and the WHO's accusation that China has vastly underreported its cases have fueled worries that the number of large SARS clusters will grow.

Which path the SARS epidemic will take depends on several factors authorities can't control, including whether the virus that causes it grows stronger or weaker as it replicates and spreads.

But measures such as quarantines could help halt the spread of the disease. So could a vaccine, although scientists say developing one will take at least a year.

`No immunity'

The coronavirus that causes SARS is part of a family that causes the common cold. It shares at least one characteristic with viral infections that have caused pandemics: It is brand new.

"One of the issues is that a strain of a virus or a bacteria hits a population with no immunity to it, and we are wide open with this - or so it seems," said Dr. Harold Standiford, medical director of infection control at the University of Maryland Medical Center.

Dr. Kenneth McIntosh, a coronavirus expert at Children's Hospital Boston, said two things must happen for the SARS virus to cause a worldwide pandemic. First, there must be a large number of people susceptible to the illness. Second, the illness must be caused by an organism capable of spreading widely.

"We have a very large number of susceptibles," McIntosh said, but the presence of the second condition is unclear. "It seemed to spread widely in Hong Kong and Hanoi, and on the other hand hasn't spread widely in other parts of the world that it's had the opportunity to do so."

Dr. Arthur L. Reingold, head of epidemiology at the University of California, Berkeley, School of Public Health, said the outbreak can be largely controlled through sound public health efforts - and a little bit of luck.

Dr. Julie L. Gerberding, director of the Atlanta-based Centers for Disease Control and Prevention, said the best-case scenario is that the virus dies out on its own.

That's unlikely, she said, but not totally implausible with the onset of spring in the northern hemisphere. Warmer weather encourages people to move outside, away from the confined spaces where disease spreads more easily.

The much-heralded swine flu fizzled out in 1976 without spreading beyond the neighborhood of Fort Dix, N.J. The Ebola virus, while lethal, is containable with careful infection control methods and "barely ekes along," according to Paul Ewald, a University of Louisville biology professor and author of the book Plague Time.